Mousetrap Car

1. Mousetrap Car • A mousetrap car is a vehicle designed to run on the energy that can be stored in a wound up mousetrap spring. • Basic design: - Attach a string to the mousetrap‘s lever arm • When lever arm is released, it pulls the string off the drive axle, causing the wheels to rotate and propelling the vehicle forward.

2. Mousetrap Car • Car must have at least 3 wheels. • Car must travel 15m and stop. • Can use any materials, but only one standard mousetrap • Original mousetrap spring and wooden base must remain intact. Bail may be straightened but not cut. • Locking lever and bait holder may be removed. • No kits allowed

3. Mousetrap Car • Potential issues: • Friction • Momentum • Center of mass • Energy • Torque

4. Mousetrap Car • Friction • Wheels and floor • Traction – too little can slip under load and decrease car’s maximum acceleration, too much and can’t accelerate • Axle and chassis • Lubricants • Bushing • Fluid friction (air resistance) • Reshape surfaces, round leading edges • Thin tires vs. wide tires • Fewer points of drag

5. Mousetrap Car • Momentum • Light cars = less momentum, heavier cars = more momentum • Heavier cars are also harder to get moving due to inertia, so pulling force must be larger and use more energy to begin acceleration. • Heavier cars also have to travel faster and experience greater fluid friction

6. Mousetrap Car • Center of Mass • Center of mass is the average position of all particles of mass that make up an object. • Objects that are forced to rotate around points that are not the center of mass consume more energy. • So be careful of your wheels – if the wheels wobble then energy is wasted and the car will not travel as far. It can also roll backwards after stopping. • If you remove mass from the wheels, you want to make sure it is balanced.

7. Mousetrap Car • Energy • Energy is the ability to do work. • Potential energy is stored energy – in this case from the wound spring. • As the spring unwinds, the potential energy is converted into kinetic energy in the form of forward motion. • You want to build a vehicle that loses energy at the lowest rate. • The more moving parts of your vehicle, the greater the energy consumption.

8. Mousetrap Car • Torque • Torque is the rotational component of force. A torque is produced when a force is exerted with leverage. • The lever arm is where you want to think about torque. • As the lever arm begins to pull the vehicle, the angle of the pulling force will change with the lever arm until the pulling angle is zero, at which point the lever arm will fall quickly without any tension in the spring. • Check the tension in the pulling string. • The lever arm needs to be properly positioned and the pulling string must pull perpendicular to the axle’s radius for maximum performance.

9. Mousetrap Car • General tips: • When you build a mousetrap car for distance, you want a small energy consumption per second or a small power usage. Smaller power outputs will produce less wasted energy and greater efficiency. • When you build a mousetrap car for speed, you want the maximum power output just before the point where the wheels begin to spin out on the floor. • Change where the string attaches to the mousetrap’s lever arm, the drive wheel diameter, or the drive axle diameter.

10. Mousetrap Car • General tips: • The amount of energy used by a short lever arm and a long lever arm are the same, but the distance that the energy is used determines that rate of energy consumption or the power. • Long lever arms decrease the pulling force, but increase the pulling distance, thereby decreasing the power. If you make the lever arm too long, you may not have enough torque through the entire pulling distance to keep the vehicle moving.

11. Mousetrap Car • General tips: • If you need more pulling force, you can shorten the lever arm (or move the string closer to the hinge) and move the mousetrap closer to the drive wheels. • If the mousetrap is placed too close to the pulling axle, the wheels may spin on the start. • The closer the center of mass is located to the drive wheels, the more traction you get.

12. Mousetrap Car